Normally speaking, in a gas bag module of a vehicle occupant restraint system, the gas bag is supposed to be inflated as quickly as possible with the gas generated by a gas generator. In certain cases, for example, in response to a collision at a relatively low speed or depending on the height, weight or position of the vehicle occupant to be protected, it is desirable to have a softer gas bag. For this purpose, for example, discharge openings can be provided in the module housing through which some of the available gas volume can escape. This solution, however, has the drawback that installation space has to be provided in the module housing for the discharge opening itself as well as possibly for an opening mechanism.
Another approach that has been known for a long time for achieving a reduced internal gas bag pressure is to provide a pleat in the wall of the non-inflated gas bag in that opposite wall sections lie against each other, the pleat being affixed by a rupture seam. If the internal gas bag pressure exceeds a predetermined value after the activation of the gas bag module, the rupture seam tears open, as a result of which the volume of the gas bag is increased and the internal gas bag pressure is reduced. It is also a known procedure to provide a discharge opening in the area of the pleat that is at first closed by the pleat and then exposed after the rupture seam tears, thus achieving a further reduction of the internal gas bag pressure.
A drawback of this known embodiment is that it does not allow the internal gas bag pressure to be adapted as a function of the situation. The rupture seam will definitely tear exactly when the internal gas bag pressure predetermined by the properties of the rupture seam has been reached.
In contrast, the invention provides a gas bag module that allows a rapid reduction of the internal gas bag pressure as a function of the momentary accident or vehicle (occupant) situation and that is nevertheless distinguished by the fact that it requires little space and is easy to manufacture.